MainFrame into singleton

        if (instance == null) {

            instance = new Controller();

			instance.model = new PlayBoard();

			instance.view = new MainFrame();

			instance.view = MainFrame.getInstance();

			instance.eventManager = new EventManager();

        }

public class MainFrame extends JFrame {

	public MainFrame() {

	private static MainFrame instance;

		FlatDarkLaf.setup();

	public static MainFrame getInstance() {

		if ( instance != null ) return instance;

		instance = new MainFrame();

		MainScreen mainScreen = new MainScreen();

		instance.setContentPane(mainScreen);

		return instance;

	}

		MainScreen mainScreen = new MainScreen(this);

		this.setContentPane(mainScreen);

	private MainFrame() {

		FlatDarkLaf.setup();

		this.setFrameIcon();

		this.setSize(1200, 800);

		this.setVisible(true);

		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

	}

	private void setFrameIcon() {

    private final MainFrame mainFrame;

    public MainScreen(MainFrame mainFrame) {

    public MainScreen() {

        this.mainFrame = mainFrame;

        this.mainFrame = MainFrame.getInstance();

        JButton btnSolo    = new JButton("SOLO");

        JButton btnMulti   = new JButton("MULTIJOUEUR");

        btnSolo.addActionListener(e -> {

            MainScreen.this.mainFrame.setContentPane(new SoloGameCreation(MainScreen.this.mainFrame));

            MainScreen.this.mainFrame.setContentPane(new SoloGameCreation());

        });

    }

}

import static view.utils.SwingUtils.*;

import java.awt.FlowLayout;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.util.Random;

import javax.swing.Box;

import javax.swing.BoxLayout;

import javax.swing.JButton;

import javax.swing.JLabel;

import javax.swing.JList;

import javax.swing.JSpinner;

import javax.swing.JTextField;

import javax.swing.event.DocumentEvent;

import javax.swing.event.DocumentListener;

import javax.swing.event.ListSelectionEvent;

import javax.swing.event.ListSelectionListener;

import main.Controller;

import main.Difficulty;

import view.MainFrame;

import view.component.Separator;

import view.listener.ResizeListener;

import view.utils.DocumentAdapter;

import view.utils.SwingUtils;

public class SoloGameCreation extends JPanel {

    private final JButton btnPlay = new JButton("Jouer");

    private final Controller controller = Controller.getInstance();

    private SoloGameScreen soloGameScreen;

    public SoloGameCreation(MainFrame mainFrame) {

    public SoloGameCreation() {

        this.setLayout(null);

		// ResizeListener resizeListener = new ResizeListener(createResizeCallback(this));

        // this.addComponentListener(resizeListener);

        btnCancel.addActionListener(e -> mainFrame.setContentPane(new MainScreen(mainFrame)));

        btnCancel.addActionListener(e -> MainFrame.getInstance().setContentPane(new MainScreen()));

        final Runnable randomSeedCallback = createRandomSeedCallback(this);

        btnRandomSeed.addActionListener(e -> randomSeedCallback.run());

		btnPlay.addActionListener(e -> {

			if (initPlayBoard()) {

				mainFrame.setContentPane(new SoloGameScreen());

				MainFrame.getInstance().setContentPane(new SoloGameScreen());

			} else {

				System.out.println("Impossible mon ga");

			}

        nbPiecesSpinner.setValue(Controller.getInstance().getPiecesCountBySeed(seed, difficulty));

    }

    private static Runnable createResizeCallback(SoloGameCreation soloGameCreation) {

        return () -> {

        };

    }

    private static long generateRandomSeed() {

        return (long) (Math.random() * Long.MAX_VALUE);

public class SoloGameFinishScreen extends JPanel {

    public SoloGameFinishScreen() {

        setLayout(null);

		super.doLayout();

    }

}